The present invention relates in general to charging devices such as utilized in electrostatographic reproduction apparatus or the like, and more particularly to a mechanism for facilitating corona wire replacement and easily and accurately tensioning the corona charger wires.
In typical commercial electrostatographic reproduction apparatus (copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged dielectric member. Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric member. A receiver member is then brought into contact with the dielectric member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric member and the image is fixed to the receiver member by heat and/or pressure to form a permanent reproduction thereon.
The electrostatic fields for various reproduction apparatus operations are commonly provided by corona charging devices. For example, corona chargers may be used to deposit the uniform charge on the dielectric member prior to light exposure, to implement transfer of a developed image from the dielectric member to a receiver member, or to neutralize charge on the dielectric member subsequent to developed image transfer to facilitate release of the receiver member or residual marking particles from the dielectric member.
Corona chargers typically include at least one very thin corona wire, located within a housing shell held at a ground potential. The corona wire is electrically coupled to a high voltage to generate ions or charging current to charge a surface (such as the dielectric member surface) brought into close proximity with the corona wire. The corona wire is tightly suspended between insulating end blocks, supported in the housing shell, such end blocks being connected to a high voltage source for producing the ion generating condition within the corona wire.
It is important that the corona wire be maintained at a tension within a particular preselected range. This is necessary because if the tension is too high, the corona wire is easily broken, and if the tension is too low the corona wire will tend to vibrate which will materially effect the ability of the wire to provide for the desired uniform charging of the intended surface. To maintain the desired tension in the corona wire, the typical corona charging device anchors the wire to one end block and connects the other end to the opposite end block through, for example, a coiled spring connector. The spring constant of the spring connector is selected to yield tension in the corona wire within the desired preselected range.
It should be well appreciated that the high voltage of the corona wire creates a corrosive environment which adversely effects the wire. That is, the atmosphere surrounding the wire is conducive to the promotion of coating and/or pitting of the wire. Over time, such action on the corona wire will cause the wire, which by its very nature is extremely fragile, to no longer be effective in producing the desired uniform charging of the surface intended to have a charge applied thereto. As such, the corona wire has to be periodically replaced. However, due to the mounting of the corona wire under tension, it has been difficult to readily effect wire replacement.
One type of corona charging device which attempts to facilitate corona wire replacement is shown in U.S. Pat. No. 4,764,675 (issued Aug. 16, 1988, in the name of Levy et al). In the corona charging device of this patent, a pivot member mounted on an end block of the device. The pivot member is movable to a first position where the corona wire can be connected to the member while untensioned, and to a second position where the wire is held under a selected tension. However, due to the space constraints with the particular arrangement of this charging device, it is still extremely difficult to attach the corona wire to the pivot member. Thus, because of the fragile nature of the wire, the attempted attachment of the wire to the pivot member may still often cause the wire to break as it is being replaced.